Technical Abstract:
Beta-D-xylosidase from Selenomonas ruminantium has been revealed as the best catalyst known for promoting hydrolysis of 1,4-beta-D-xylooligosaccharides, and it has potential utility in saccharification processes. Kinetic parameters, kcat and kcat/Km, are more than 10-fold larger than those reported for the enzyme isolated from other organisms. In cleaving 1,4 glycosidic bonds, the family 43 glycoside hydrolase acts through an inversion mechanism and cleaves a single xylose residue from the nonreducing end of xylooligosaccharides per catalytic cycle without processivity. Three-dimensional structures of homologous GH43 xylosidases indicate that the enzyme active site has only two subsites for recognition of substrate, the two terminal xylosyl residues that share the scissile glycosidic bond. In addition to its xylosidase activity, the enzyme efficiently catalyzes hydrolysis of 4-nitrophenyl-alpha-L-arabinofuranoside. Temperature dependence of kinetic parameters of enzyme-catalyzed reactions and noncatalyzed reactions were determined.